Beryllium copper, also known as copper beryllium, BeCu or beryllium bronze, is a metal alloy of copper and 0.5 to 3% beryllium, and sometimes with other alloying elements.Alloy 25 is also known as “CuBe2, C17200, BeCu, CDA 172, CB101, ISO CuBe2, CEN CW101C, A4/2, beryllium bronze”.